An All-metal Capacitive Coupling Structure for Coaxial Cavity Filters

In this paper, a novel capacitive coupling structure for coupled resonator filters is proposed and experimentally verified. Instead of using a metal dumbbell probe that is pinched by a PTFE dielectric block for electrical coupling, the proposed coupling structure uses a dumbbell probe that is mounted on a grounded metal 'lamp-pole' stand. This all-metal structure is mechanically and thermally stable and is with a high power handling capability. The circuit model of the coupling structure is analyzed to reveal the basic electrical properties of the coupling structure. In addition to an EM designed 6-pole coaxial resonator filter with two TZs, a 3-pole prototype filter with one transmission zero (TZ) is manufactured and tested to demonstrate that the proposed coupling structure can be a viable option in realizing capacitive cross couplings in coaxial resonator filters.